Metal condensed phosphate hardener coated with reaction product from a metal aluminate and/or a metal borate

ABSTRACT

Disclosed is a metal condensed phosphate comprising a core of metal condensed phosphate and a coating on the core comprising a reaction product of a metallate and acid. The amount of the reaction product comprising the coating generally ranges from about 0.1 percent to about 50 percent by weight based on the combined weight of the metal condensed phosphate and the reaction product. 
     Also disclosed is a method of preparing a coated, metal condensed phosphate comprising combining an aqueous slurry of metal condensed phosphate with an aqueous metallate while maintaining the pH of the slurry in a range of from about 4 to about 10.

This is a division of application Ser. No. 260,228, filed May 4, 1981.

BACKGROUND OF THE INVENTION

Environmental pollution concerns have led those in the coatings andresins arts to develop curable compositions from which organic solventshave been eliminated or at least substantially reduced. Moreover, thehigh cost and scarcity of petroleum by-products has generated interestin the development of curable compositions based entirely, or at leastsubstantially, on inorganic components.

Inorganic coating compositions based on alkali metal silicates andinorganic phosphate hardeners are known. However, when alkali metalsilicates and inorganic phosphate hardeners are mixed, they tend torapidly coagulate, solidify or the like due to the strong reactivitybetween the silicate and the phosphate. Thus compositions based onalkali metal silicates and metal phosphate hardeners tend to haverelatively short useful lives. Additionally, due to this strongreactivity, generally known alkali silicate/phosphate hardenercompositions generally contain undesirable particles or lumps. Suchparticles or lumps interfere, for example, in spraying applicationsemploying compositions containing these particles or lumps. Furthermore,cured coatings produced from such compositions contain highlyundesirable lumps.

Applicants' copendings application Ser. No. 218,861 filed Dec. 22, 1980,U.S. Pat. No. 4,319,926, discloses an aqueous curable compositioncontaining an alkali metal silicate and an aqueous dispersion of a metalcondensed phosphate hardener containing an amount of base sufficient toraise the pH of the hardener dispersion to a value greater than 9.5.Such compositions containing the specified amount of base cure tosmooth, essentially lump-free, durable coatings.

The present invention is directed to curable inorganic coatingcompositions based on water-soluble and/or water-dispersible alkalimetal silicates which have extended useful lives. Further objects of thepresent invention will become apparent in the description of theinvention.

SUMMARY OF THE INVENTION

The present invention provides for a coated, metal condensed phosphateuseful for hardening water-dispersible and/or water-soluble alkali metalsilicates. The coating on the metal condensed phosphate comprises areaction product from a water-soluble and/or water-dispersible metallateand acid. The water-soluble and/or water-dispersible metallate isselected from the group consisting of a metal aluminate and a metalborate.

The invention also provides for a method for preparing the coated, metalcondensed phosphate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a coated, metal condensed phosphatecomprising a core of a metal condensed phosphate and a coating on thecore comprising a reaction product of a water-soluble and/orwater-dispersible, preferably water-soluble, metallate and acid. Themetallate is selected from the group consisting of a metal aluminate anda metal borate. The acid component may be the acid due to the metalcondensed phosphate itself. The acid component also may be an additionalacid independently combined with the metal condensed phosphate andwater-soluble and/or water-dispersible metallate. The amount of thereaction product of the aqueous metallate and acid on the metalcondensed phosphate ranges from about 0.1 percent to about 50 percent byweight, typically from about 1 percent to about 15 percent by weight,based on the combined weight of the metal condensed phosphate and theaforementioned reaction product.

The invention also provides for a method of preparing a coated metalcondensed phosphate comprising:

(A) combining an aqueous slurry of metal condensed phosphate with

(B) an aqueous solution and/or dispersion, preferably a solution, of ametallate selected from the group consisting of a metal aluminate andmetal borate, the metallate being in an amount sufficient to provide acoating on the metal condensed phosphate of from about 0.1 percent toabout 50 percent by weight, typically from about 1 percent to about 15percent by weight, based on the combined weight of the metal condensedphosphate and the coating.

Generally the aqueous metallate is combined with the slurry of metalcondensed phosphate while the pH of the slurry ranges from about 4 toabout 10. For example, when an aqueous metal aluminate is combined withthe aqueous slurry of metal condensed phosphate without the use ofadditional acid, the slurry temporarily can become quite basic asevidenced by pH values as high as about 10. However, when an additionalacid is combined with the slurry of metal condensed phosphate and theaqueous metal aluminate, the pH of the slurry typically ranges fromabout 6 to about 8. Generally the combination of the aqueous slurry ofmetal condensed phosphate and the aqueous metallate is carried out whilemaintaining the temperature of the slurry in a range of from about 25°C. to about 95° C., preferably from about 50° C. to about 95° C., andmost preferably from about 80° C. to about 95° C. Specific ways ofpreparing a coated metal condensed phosphate of the invention inaccordance with the method of the invention will be described infra.

The core of metal condensed phosphate may be any metal condensedphosphate generally known for use in silicate-based inorganic paints orcoating compositions. The metal condensed phosphate may be prepared, forexample, by dehydration of one or more ortho phosphates at about 300° toabout 1200° C. For example, condensed aluminum phosphate may be preparedby evaporating an aqueous 30 percent by weight Al(H₂ PO₄)₃ solution todryness and heating the resulting material to a temperature of about400° C. to 500° C. Another example of a method of preparation of acondensed aluminum phosphate, described in U.S. Pat. No. 3,943,231, isto spray-dry a relatively dilute solution or suspension of an aluminumorthophosphate containing P₂ O₅ and Al₂ O₃ in the molar ratio desired inthe final product at temperatures higher than 250° C. to effect directtransformation into condensed aluminum phosphates. German Pat. No.1,252,835 describes a method for obtaining condensed aluminum phosphateswherein an aluminum phosphate solution is evaporated to dryness and theresulting material subjected to a two-step heat treatment at differenttemperatures. Finally, methods for preparing condensed iron phosphatesand condensed aluminum phosphates are described in the Bulletin of theSociete Chemique deFrance, article No. 37, (1961), pages 2277-2282 andthe Bulletin of the Societe Chemique deFrance, article No. 221, (1962),pages 1237-1243.

Metal condensed phosphates used as the core in the present inventiontypically comprise condensed aluminum phosphates. Various condensedaluminum phosphates, including their methods of preparation, aredescribed, for example, by d'Yvoire in the Bulletin of the SocieteChemique deFrance, (1961), article No. 337, at 2277-2282 and thebulletin of the Societe Chemique deFrance, (1962), article No. 221 at1237-1243 wherein a cyclic aluminum tetrametaphosphate, (i.e., theA-form of Al(PO₃)₃) and four long-chain polyphosphates, (i.e., the B-,C-, D- and E-forms of Al(PO₃)₃) are identified. As reported by d'Yvoire,these condensed aluminum phosphates may be produced, for example, byreacting P₂ O₅ and Al₂ O₃ in a molar ratio respectively of from 4:1 to15:1. U.S. Pat. No. 4,216,190, hereby incorporated by reference,describes a method for making B-form aluminum trimetaphosphate by theaddition of concentrated ammonium hydroxide to a solution of aluminumdihydrogen phosphate, Al(H₂ PO₄)₃, to effect the formation of a whiteprecipitate which is directly converted to the B-form aluminumtrimetaphosphate, Al(PO₃)₃, by a single elevated temperature treatment.

When a condensed aluminum phosphate is used as the core in the presentinvention, it generally comprises a linear condensed aluminum phosphate,namely one or more of the long-chain polyphosphates (i.e., the B-, C-D-, and E-forms of Al(PO₃)₃). Also, a mixture of A-form aluminummetaphosphate with one or more of the long-chain aluminum polyphosphates(i.e., the B-, C-, D- and E-forms of Al(PO₃)₃) may be used in thepresent invention as the core of metal condensed phosphate. When amixture comprising A- and B-form aluminum metaphosphates is used as thecore, the weight ratio of the B-form to A-form aluminum metaphosphategenerally ranges from about 3:5 to about 4:1, preferably from about 7:3to about 4:1.

In accordance with the present invention, the coating on the core ofmetal condensed phosphate comprises a reaction product of acid and awater-soluble and/or a water-dispersible metal aluminate or metalborate. A mixture of metal aluminate and metal borate, of course, isconsidered to be within the scope of the present invention. The acid maybe any acid suitable for applying the coating to the core of metalcondensed phosphate in accordance with the invention. The metalcondensed phosphate in a dispersion of metal condensed phosphate tendsto make the dispersion acidic. The reaction of the acid inherentlypresent in such a dispersion of metal condensed phosphate with aqueousmetallate, even without addition of any further acid, preferably is usedto apply the coating to the core of metal condensed phosphate. Forexample, in a preferred embodiment, the dispersion of metal condensedphosphate is combined with aqueous metal aluminate without the additionof any further acid. However, an additional acid or mixture of acids canbe combined with the metal condensed phosphate and aqueous metallate toapply the coating to the metal condensed phosphate. Examples of suitableadditional acids include: phosphoric acid, sulfuric acid, hydrochloricacid, hydrobromic acid, hydroidic acid, nitric acid, perchloric acid,chloric acid, methane sulfonic acid, ethane sulfonic acid,trichloroacetic acid, and trifluoroacetic acid. When said additionalacid is used phosphoric acid is preferred.

The metallate suitable for the present invention may be any watersoluble and/or water-dispersible metallate or mixture of metallatesselected from the group consisting of metal aluminates and metalborates. Metal aluminates, particularly water-soluble metal aluminatesare preferred. When metal borates are used in the invention,water-soluble metal borates are preferred.

Examples of suitable metal aluminates include sodium aluminate,potassium aluminate, and calcium aluminate. Typically sodium aluminateis used. A typical sodium aluminate solution useful in the presentinvention may be prepared by dissolving enough sodium aluminate in waterto obtain about a 30 to 40 percent by weight sodium aluminate solution.Of course, metal aluminate solutions of higher or lower concentrationthan 30 to 40 percent by weight are considered to be within the scope ofthe present invention. Examples of suitable metal borates include sodiummetaborate, potassium metaborate, sodium tetraborate, and potassiumtetraborate. When a metal borate is used in the invention, typicallysodium borate is used.

Any metal condensed phosphate comprising a core of metal condensedphosphate and a coating on the core comprising a reaction product ofacid and a metallate selected from the group consisting of metalaluminate, metal borate and a mixture thereof, however the coating isapplied, is considered to be within the scope of the invention. Sometypical methods of coating the metal condensed phosphate will bedescribed.

In a first embodiment of the invention, an aqueous slurry of the metalcondensed phosphate, an aqueous metal aluminate, and an additional acidas previously described are combined so as to maintain the pH of theslurry in a range of from about 4 to about 10, typically from about 6 toabout 10, while maintaining the temperature of the slurry in a range offrom about 25° C. to about 95° C., typically from about 50° C. to about95° C., and usually from about 80° C. to about 95° C. In this embodimentthe aqueous metal aluminate typically is slowly added to the aqueousslurry of metal condensed phosphate. However, the addition of theaqueous slurry of metal condensed phosphate to the aqueous metalaluminate is considered to be within the scope of the invention. Theadditional acid such as those described previously typically is slowlyadded to the slurry of metal condensed phosphate during at least part ofthe addition of the aqueous metal aluminate.

Although the coated metal condensed phosphate may be prepared using anaqueous slurry of metal condensed phosphate at room temperature,typically, in the first embodiment, the aqueous slurry of metalcondensed phosphate initially is heated to a temperature ranging fromabout 50° C. to about 95° C., preferably from about 80° C. to about 95°C., and the pH of the slurry is adjusted to a pH generally ranging fromabout 4 to about 10, typically ranging from about 6 to about 8, beforecombining the aqueous slurry of metal condensed phosphate with theaqueous metal aluminate. This initial pH adjustment may be carried outconcurrently with or separately from the heating step. Typically theslurry of metal condensed phosphate is heated while the pH is adjusted.The adjustment of pH as described above facilitates mixing of the metalcondensed phosphate with the aqueous metal aluminate by increasing thefluidity of the aqueous metal condensed phosphate.

The initial adjustment of the pH of the slurry of metal condensedphosphate in the above method can be carried out using an aqueous alkalihydroxide such as sodium or potassium hydroxide. However it is preferredto initially adjust the pH of the slurry of metal condensed phosphateusing a basic, water-soluble metal aluminate itself.

To the above slurry of metal condensed phosphate, the aqueous metalaluminate slowly is added, at least in part along with the additionalacid, so as to maintain the pH in the rage of from about 4 to about 10,typically from about 6 to about 8, and while maintaining the temperaturein the range of from about 25° C. to about 95° C., preferably from about50° C. to about 95° C., and most preferably from about 80° C. to about95° C. The amount of metal aluminate will be determined by the desiredweight of the reaction product to be deposited on the metal condensedphosphate, generally an amount sufficient to provide a coating on themetal condensed phosphate ranging from about 0.1 percent to about 50percent by weight, typically from about 1 percent to about 15 percent byweight, based on the combined weight of the metal condensed phosphateand the coating. The amount of additional acid typically added is thatamount to maintain the pH in the previously described range. It isbelieved that when the additional acid is employed with the aqueousmetal aluminate to coat the metal condensed phosphate, at least part ofthe coating on the condensed phosphate, and probably a substantial part,results from the reaction of the metal aluminate with the additionalacid.

Near the end of the addition of the aqueous metal aluminate to theaqueous slurry of metal condensed phosphate, if desired, the addition ofacid may be stopped so that the pH of the slurry after the addition ofthe metal aluminate will range from about 7.5 to about 8.0. Alternately,if acid is added concurrently with the metal aluinate until all themetal aluminate has been added, and if the pH is then not in the rangeof from about 7.5 to about 8.0, where desired, a base such as aqueousalkali hydroxide may be added to raise the pH into the range of fromabout 7.5 to about 8.0.

In a preferred, second embodiment of the invention, the aqueous metalaluminate, preferably in the form of a solution, simply is slowlycombined with the aqueous slurry of metal condensed phosphate so thatthe pH of the slurry during the combination varies within a range offrom about 4 to about 10. No additional acid is combined with theaqueous slurry of metal condensed phosphate and the aqueous metalaluminate in this particular embodiment of the invention. The aqueousmetal aluminate is combined with the aqueous slurry of metal condensedphosphate while maintaining the temperature of the slurry in a range offrom about 25° C. to about 95° C., preferably from about 50° C. to about95° C., and most preferably from about 80° C. to about 95° C. In thisembodiment of the invention, the coating on the metal condensedphosphate is believed to be at least in part the reaction product of themetal aluminate and acid from the acidic metal condensed phosphateitself. As in the previously described embodiment, the amount of metalaluminate employed will be determined by the desired weight of thereaction product to be deposited on the metal condensed phosphate,generally an amount sufficient to provide a coating on the metalcondensed phosphate ranging from about 0.1 percent to about 50 percentby weight, typically from about 1 percent to about 15 percent by weight,based on the combined weight of the metal condensed phosphate and thecoating.

Although the coated metal condensed phosphate may be prepared using anaqueous slurry of metal condensed phosphate at room temperature,typically in this second embodiment of the invention, the aqueous slurryof metal condensed phosphate initially is heated to a temperatureranging from about 50° C. to about 95° C., preferably from about 80° C.to about 95° C. As in the previously described method, the pH of theslurry of metal condensed phosphate typically is adjusted to a pHranging from about 4 to about 10, usually from about 6 to about 8, whilethe slurry initially is heated to the aforementioned temperature range.This initial pH adjustment of the slurry of metal condensed phosphatecan be carried out using an aqueous alkali hydroxide or, preferably,using a basic, water-soluble metal aluminate itself.

In a third embodiment of the invention, an aqueous slurry of the metalcondensed phosphate, an aqueous metal borate, and an additional acid aspreviously described are combined according to the procedures set forthin the description of the first embodiment above except that an aqueousmetal borate, typically aqueous sodium metaborate, is substituted forthe aqueous metal aluminate in the first embodiment.

In a fourth embodiment of the invention, an aqueous metal boratepreferably in the form of a solution, simply is slowly combined with theaqueous slurry of metal condensed phosphate so that the pH of the slurryduring the combination varies within a range of from about 4 to about10. No additional acid is combined with the aqueous slurry of metalcondensed phosphate and the aqueous metal borate in this particularembodiment of the invention. The procedures for combining the aqueousslurry of condensed phosphate and aqueous metal borate in thisembodiment are set forth in the description of the second embodimentabove except that an aqueous metal borate is substituted for the aqueousmetal aluminate in the second embodiment.

The coated, metal condensed phosphate of the invention is useful as asilicate hardener in aqueous compositions containing water-solubleand/or water-dispersible silicate such as silicate based cements andespecially silicate based coating compositions. Such silicates typicallycomprise water-soluble and/or water-dispersible alkali metal silicateshaving a SiO₂ :M₂ O mole ratio ranging from about 2.0:1.0 to about4.0:1.0, preferably from about 3.3:1.0 to about 3.5:1.0, wherein Mrepresents the alkali metal. Of the above silicates, water solublealkali metal silicates, particularly potassium silicate, are preferred.A typical aqueous coating composition containing a coated, metalcondensed phosphate of the invention would comprise (A) from about 10 toabout 45 percent, preferably from about 10 to about 32 percent, and mostpreferably from about 15 to about 25 percent by weight of water-solubleand/or water-dispersible silicate (solids); (B) from about 2.0 to about32 percent, preferably from about 2 to about 10 percent, and mostpreferably from about 8 to about 10 percent by weight of a metalcondensed phosphate hardener (solids); and (C) water. The water incomponent (C) includes all water in the aqueous coating composition fromany source. For example, the water in component (C) is intended toinclude the water present in generally known aqueous alkali silicatetypically used to prepare a coating composition. The water in component(C) also is intended to include, for example, water present in anaqueous dispersion of metal condensed phosphate typically used toprepare a coating composition. Where desired, the aqueous coatingcomposition also may contain generally known pigments, fillers,additives or mixtures thereof. The metal condensed phosphate hardenerwould comprise a core of metal condensed phosphate and a coating on thecore in accordance with the present invention.

Although the above alkali metal silicates are preferred in aqueouscoating compositions containing water-soluble and/or water-dispersiblesilicates and coated, metal condensed phosphate of the invention,water-soluble and/or water-dispersible alkali metal silicates which havebeen modified with an oxide or a hydroxide of a metal such as Al, Ca,Mg, Zr, V, Zn or Cs may also be used as the silicate component. Oxide-or hydroxide-modified silicates may be obtained, for example, by mixingan aqueous solution of the appropriate metal oxide or metal hydroxidewith the aqueous silicate and heating the mixture while stirring.Usually, the heating is conducted at about 50° to 100° C. for about 1 to72 hours. However, if the reaction is conducted in a pressure vessel ata temperature higher than 100° C., the reaction time may be shorter. Theamount of oxide or hydroxide may be 0.5 to 3.0 parts by weight per 100parts by weight (based on dry solids without water of crystallization)of the silicate.

The amount of coated condensed metal phosphate hardener (solids) inthese aqueous curable compositions ranges from about 2.0 to about 32percent, preferably from about 2 to about 10 percent, and mostpreferably from about 8 to about 10 percent by weight based on totalweight of the composition. The weight ratio of total alkali metalsilicate solids to condensed metal phosphate solids, respectively, inthese compositions generally ranges from about 1.0:1.0 to about10.6:1.0, preferably from about 1.7:1.0 to about 10.6:1.0, and mostpreferably from about 1.9:1.0 to about 2.6:1.0.

The silicate based aqueous curable compositions may be prepared bymixing the water-soluble and/or water-dispersible silicate with thecoated metal condensed phosphate hardener. When desired, a water-solublebase may be mixed with an aqueous dispersion of the condensed phosphatehardener prior to combining the hardener with the silicate. Thewater-soluble base is mixed with the aqueous dispersion of condensedphosphate hardener until the pH of the mixture is at least 9, preferablygreater than 9.5, and most preferably at least 10. A curable compositionis then formed by mixing the aqueous dispersion of coated condensedphosphate and the water-soluble and/or water-dispersible silicate whilethe pH of the dispersion of condensed phosphate is at an appropriatevalue described above. Examples of bases which may be used to raise thepH of the aqueous dispersion of condensed phosphate include: alkalimetal hydroxides such as sodium hydroxide, potassium hydroxide andlithium hydroxide; quaternary ammonium hydroxides such as tetraethylammonium hydroxide and tetra-ethanol ammonium hydroxide; ammonia; aminessuch as triethylamine and 3-(diethylamino)propan-1-ol; tertiarysulfonium hydroxides such as trimethyl sulfonium hydroxide and triethylsulfonium hydroxide; quaternary phosphonium hydroxides such astetramethyl phosphonium hydroxide and tetraethyl phosphonium hydroxide;organosilanolates such as tripotassium-γ-aminopropylsilantriolate,tripotassium N-(β-aminoethyl)-γ-aminopropylsilantriolate, dipotassiumdimethylsilandiolate, potassium trimethylsilanolate,bis-tetramethylammonium dimethylsilandiolate, bis-tetraethylammoniumdimethylsilandiolate and tetraethylammonium trimethylsilanolate; andmixtures thereof. Of the bases described above, alkali metal hydroxides,quaternary ammonium hydroxides, ammonia and amines are preferred when itis desired to mix a water-soluble base with the dispersion of condensedphosphate. The alkali metal hydroxides are particularly preferred.

When a base such as those described immediately above is used in asilicate based, aqueous curable composition, the percent by weight ofsuch base in the composition generally ranges from about 0.2 percent toabout 0.8 percent, preferably from 0.2 percent to about 0.5 percent,based on the total weight of the composition. As discussed previously,the bases are mixed with the aqueous dispersion of coated condensedphosphate hardener before the condensed phosphate hardener is admixedwith the water-soluble and/or water-dispersible silicate.

The amount of water in the silicate based, aqueous curable compositionsmay vary widely depending on the intended use. Generally, the aqueousphase of the compositions contains up to 90 percent by weight water,typically from about 42 percent to about 64 percent by weight water, andpreferably from about 50 percent to about 60 percent by weight water.

As previously stated, such aqueous curable coating compositionscontaining water-soluble and/or water dispersible silicate and coated,metal condensed phosphate of the invention also may contain generallyknown pigments, fillers, additives or mixtures thereof. Generally,pigments, fillers, additives or mixtures thereof may be used in theseaqueous curable coating compositions in amounts up to 80 percent byvolume solids, typically from about 32 percent to about 80 percent byvolume solids, and preferably from about 50 percent to about 60 percentby volume solids, based on the total volume of solids present in thecomposition.

Examples of pigments suitable for coating compositions containing acoated, metal condensed phosphate of the invention and silicate include:titanium dioxide, iron oxide red, iron oxide black, manganese black andcarbon black. Mixtures of pigments also may be used. A particularlypreferred pigment is titanium dioxide coated with alumina available asR-900 from E. I. duPont de Nemours & Company. When desired, pigments tobe employed in coating compositions containing silicate and a coated,metal condensed phosphate of the invention also may be coated with thereaction product of water-soluble and/or water-dispersible metallate andacid either separately from or concurrently with the metal condensedphosphate. Coating compositions containing such coated pigments wouldappear to have even longer useful lives (for example 8 days or more)than coating compositions containing silicate, coated, metal condensedphosphate of the invention, and uncoated pigment.

Aqueous coating compositions containing water-dispersible and/or watersoluble silicate and coated, metal condensed phosphate of the inventiongenerally have useful lives of at least 8 hours, preferably up to 24hours, and some compositions in excess of 60 hours. By "useful life" ofa coating composition is meant the period in which an aqueous coatingcomposition containing water-soluble and/or water dispersible silicateand coated, metal condensed phosphate of the invention remainssubstantially lump-free and sprayable such that a cured coating issubstantially lump-free. Cured coatings prepared from compositionscontaining coated metal condensed phosphate of the invention areresistant to high temperatures, water, detergents and cracking.

Fillers which may be used in silicate based coating compositionscontaining coated, metal condensed phosphate of the invention includeinert fillers and/or reinforcing fillers generally known in the art.Examples of such fillers include: silica, mica, clay, sand, glass fibersand steel fibers. The fillers may be incorporated at any stage of theformulation of the compositions.

Additives which may be used in silicate based coating compositionscontaining coated, condensed phosphate of the invention includegenerally known additives such as dyes, defoamers, release agents,anti-mar agents, flow control agents, surfactants, thickeners,fungicides and mildewcides. These various additives may be incorporatedat any stage in the formulation of the compositions.

Coating compositions employing the coated, metal condensed phosphates ofthe invention have a variety of applications. They are particularlyuseful where high temperature, water and detergent resistanc aredesired. They may be applied to a wide variety of substrates including,for example, wood, metal, glass, wallboard, cement and the like. Suchcoating compositions are particularly useful as relatively lowtemperature curing substitutes for porcelain in appliances. The coatingcompositions may be applied by any known method including, for example,brushing, dipping, rolling, flow coating, doctor roll coating, sprayingand the like. Generally known spray techniques and equipment may beutilized.

Coating compositions employing the coated, metal condensed phosphates ofthe invention can be cured at moderate or elevated temperatures. Theymay be air dried at ambient atmospheric temperatures, but coatingcompositions so cured are not as water resistant, detergent resistantand crack free as when cured at moderate or elevated temperatures.Generally silicate based coating compositions containing coated, metalcondensed phosphate of the invention can be cured in relatively shortperiods of time at temperatures as low as about 100° C., typically aslow as about 200° C., to form smooth, substantially lump-free, durableheat-, water-, and detergent-resistant coatings. For example such acoating composition having a wet film thickness of about 6 mils on asteel substrate, after being air dried, typically can be cured to adurable dry coating of about 3 mils in about 60 minutes or less at about220° C. or less.

The following examples illustrate the invention. Amounts and percentagesare by weight unless specified otherwise. When used herein, "pbw" means"parts by weight."

When used to describe the results of a given test, the word, "passed,"means that at the end of the test, the coating shows no evidence ofdeterioration.

EXAMPLE I (Preparation of a Coated, Aluminum Metaphosphate)

(a) An aqueous slurry is prepared from 300 grams (g) of HB hardeneravailable from Pennwalt Company (containing about 80% by weight B-formaluminum metaphosphate and about 20% by weight A-form aluminummetaphosphate), 75 g A-form aluminum metaphosphate, and 600 milliliters(ml) water. The above materials are mixed for about 16 hours in a ballmill to produce a slurry containing 37.5% by weight solids and having apH of 2.4 at 25° C.

(b) 475 g of the slurry from part (a) immediately above is heated to 90°C. while stirring. Then enough aqueous, 50% by weight sodium hydroxideis added to raise the pH into the range of from 6 to 8.

Next an aqueous 42.5% by weight sodium aluminate solution and an aqueous96% by weight sulfuric acid solution are simultaneously added dropwiseto the slurry while the slurry is stirred and the temperature maintainedin the range of from 85° C. to 95° C. The simultaneous dropwise additionof the sodium aluminate and sulfuric acid solutions is carried out sothe pH of the slurry is maintained in the range of from 6 to 8. A totalof 22.8 ml of the 42.5% sodium aluminate solution is used during theaddition.

Then the pH of the slurry is adjusted to within the range of 7.5 to 8.The slurry is then filtered and washed with water until no sulfate ionsare detectable through precipitation by an aqueous barium chloridesolution. The solid product is dried at 120° C. 189.5 g of dry, coatedaluminum metaphosphate is obtained.

EXAMPLE 2 (Preparation of a Curable Coating Composition and a CuredCoating)

(a) An aluminum metaphosphate hardener is prepared by mixing thecomponents set forth in the following TABLE I.

                  TABLE 1                                                         ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Coated aluminum metaphosphate of                                                                   165.7                                                    EXAMPLE 1                                                                     Water                266.9                                                    Aqueous 50% KTPP.sup.1                                                                             20.9                                                     Strodex PK-90.sup.2  3.6                                                      Strodex SEK-50.sup.3 6.5                                                      Foamaster VL.sup.4   2.3                                                      Attagel 40.sup.5     14.7                                                     Micromica C-1000.sup.6                                                                             94.4                                                     Minusil-10.sup.7     20.9                                                     Pigment.sup.8        143.6                                                    ______________________________________                                         .sup.1 A 50% solution of potassium tripolyphosphate.                          .sup.2 A proprietary surfactant available from Dexter Chemicals Corp.         containing 90% solids comprising potassium salts of organophosphates.         .sup.3 A proprietary surfactant available from Dexter Chemicals Corp.         containing 50% solids comprising potassium salts of organophosphates.         .sup.4 An antifoaming agent available from Diamond Shamrock Corp.             .sup.5 A clay additive available from Englehard Minerals Corp.                .sup.6 Mica available from English Mica Corp.                                 .sup.7 A silica extender available from PGS Corp.                             .sup.8 Shepherd Black #1 available from Shepherd Chemical Co.            

The pH of the mixture is then adjusted to 10.5 with 12.7 pbw of anaqueous 50% by weight solution of potassium hydroxide. The resultantmaterial is an aluminum metaphosphate hardener herein designated 2A.

(b) A curable coating composition containing 46.5% solids hereindesignated 2C is prepared by mixing the components set forth in thefollowing TABLE 2.

                  TABLE 2                                                         ______________________________________                                                         Composition 2C                                                                (pbw)                                                        ______________________________________                                        Hardener 2A        731.9                                                      Water              78.8                                                       Aqueous sodium silicate.sup.1                                                                    698.7                                                      Aqueous potassium silicate.sup.2                                                                 349.4                                                      ______________________________________                                         .sup.1 Contains 37.9% solids; mole ratio of SiO.sub.2 /Na.sub.2 O = 3.40      .sup.2 Contains 38.8% solids; mole ratio of SiO.sub.2 /K.sub.2 O = 3.30  

The curable composition, 2C, remains liquid and sprayable even after twodays.

(c) Several steel panels are sprayed with the curable coatingcomposition, 2C, two days after the composition is prepared. The wetfilms are essentially lump-free and have a thickness of about 6 mils.The films are allowed to air dry at ambient temperature and then arecured at 220° C. for about 1 hour to durable, essentially lump-freecoatings of approximately 3 mils thickness.

The cured coatings on the panels are subjected to the following testswith the indicated results.

The coating on a panel is scored in a cross-hatched configuration andtape is applied to the scored coated surface. Upon ripping the tapequickly from the panel, the coating remains intact thereby exhibitingexcellent adhesion to the panel.

After being heated at 538° C. for 1 hour, the coating on another panelshows no evidence of deterioration.

The coating on a panel is scored and the panel is placed in a humiditycabinet at 100% condensing humidity at 37.8° C. according to ASTMD1735-60T as described in Paint Testing Manual by Gardener and Sward,(1962). The coating shows no evidence of deterioration after 1000 hoursin the humidity cabinet.

A panel is placed in a 15 gallon detergent tank containing a detergentformulation at 74° C. The detergent formulation contains 505 g sodiumtetrapyrophosphate decahydrate, 107.7 g anhydrous sodium sulfate, 39.7 gsodium metasilicate, 5.7 g anhydrous sodium carbonate, 113.4 g sodiumalkylarylsulfonate (available from Fisher Scientific Company as S-198)and enough water to fill 15 gallons (56.8 liters). After 500 hours inthe detergent tank, the coating shows no evidence of deterioration.

A panel is placed in a 5% by weight salt spray according to ASTM B 117described in Paint Testing Manual by Gardener and Sward, (1962). Thecoating shows no evidence of deterioration after 1000 hours at 35° C. inthe salt spray.

Another coated panel is submersed in water at 93° C. After about 48hours in the water the panel shows no evidence of deterioration.

The following EXAMPLE 3 illustrates the invention using an even lightercoating on the aluminum metaphosphate than in EXAMPLE I and the use ofphosphoric acid instead of sulfuric acid.

EXAMPLE 3 (Preparation of a Coated, Aluminum Metaphosphate)

(a) An aqueous slurry is prepared from 280 g HB hardener, 70 g A-formaluminum metaphosphate, and 400 ml water by milling the components in aball mill for 4 hours. When milling is complete, an additional 100 mlwater is added to the mixture to produce a slurry containing 41.1% byweight solids and having a pH of 2.7.

(b) Two, separate 425 g portions of the slurry of part (a) immediatelyabove, herein designated 3S and 3S' respectively, are each heated to 90°C. while stirring. Then enough aqueous, 50% by weight sodium hydroxideis added to each slurry to raise the pH into the range of from 6 to 8.

While stirring portion 3S and maintaining the temperature at 90°±4° C.,6.7 g (4.3 ml) of aqueous 42.5% by weight sodium aluminate and alsoaqueous 85% by weight phosphoric acid simultaneously are added dropwise.The pH is maintained in the range of 6 to 8 during the dropwiseaddition. The phosphoric acid addition is stopped just before theaddition of sodium aluminate is stopped, and the remaining several dropsof sodium aluminate are added to adjust the pH to 7.5. Portion 3S isthen cooled. The resultant composition herein designated 3A contains32.6 percent by weight solids and has a pH after cooling to 20° C. of6.8.

Portion 3S' is treated in the same manner as portion 3S above exceptthat 17.0 g (11.0 ml) of aqueous 42.5% by weight sodium aluminate isused. The resultant composition, herein designated 3A', contains 31.1%by weight solids and has a pH after cooling to 20° C. of 6.3.

EXAMPLE 4 (Preparation of Two Curable Coating Compositions and Two CuredCoatings Therefrom)

(a) Two aluminum metaphosphate hardeners herein designated 4A and 4A'respectively are prepared by mixing the components set forth in thefollowing TABLE 3.

                  TABLE 3                                                         ______________________________________                                                        Hardener 4A                                                                            Hardener 4A'                                                         (pbw)    (pbw)                                                ______________________________________                                        Coated aluminum metaphosphate,                                                                  531.8      --                                               3A, of Example 3(b)                                                           Coated aluminum metaphosphate,                                                                  --         519.1                                            3A', of Example 3(b)                                                          Aqueous 50% KTPP* 10.5       10.5                                             Strodex PK-90*    7.3        7.3                                              Foamaster VL*     2.3        2.3                                              Attagel 40*       14.7       14.7                                             Micromica C-1000* 47.2       47.2                                             Minusil-10*       20.9       20.9                                             TiO.sub.2 pigment**                                                                             110.6      110.6                                            ______________________________________                                         *Described in EXAMPLE 2(a).                                                   **A titanium dioxide pigment coated with alumina available as R900 from E     I. duPont de Nemours and Company.                                        

(b) Hardener 4A is mixed with 2.28 pbw aqueous 50% by weight potassiumhydroxide to a pH of 10.4. Then a curable coating composition containing44.2% by weight solids, herein designated 4C, is prepared by mixing thecomponents set forth in the following TABLE 4.

In a similar manner, hardener 4A' is mixed with 3.8 pbw aqueous 50% byweight potassium hydroxide to a pH of 10.5. Then a curable coatingcomposition containing 43.9% by weight solids, herein designated 4C', isprepared by mixing the components set forth in the following TABLE 4.

                  TABLE 4                                                         ______________________________________                                                      Composition 4C                                                                          Composition 4C'                                                     (pbw)     (pbw)                                                 ______________________________________                                        Hardener 4A of Example                                                                        747.6       --                                                4(b)                                                                          Hardener 4A' of Example                                                                       --          736.4                                             4(b)                                                                          Water           32.1        32.1                                              Aqueous sodium silicate*                                                                      698.7       698.7                                             Aqueous potassium silicate*                                                                   349.4       349.4                                             Micromica C-3000**                                                                            47.2        47.2                                              ______________________________________                                         *Described in EXAMPLE 2(b)                                                    **Mica available from English Mica Corp.                                 

(c) Several steel panels, collectively designated PC, are sprayed to awet film thickness of about 6 mils with coating composition 4C shortlyafter composition 4C is prepared. The wet films are essentiallylump-free.

Several steel panels, collectively designated P₂₄ C, are sprayed to awet film thickness of about 6 mils with coating composition 4Ctwenty-four hours after composition 4C is prepared. The wet films areessentially lump-free.

Several steel panels, collectively designated PC', are sprayed to a wetfilm thickness of about 6 mils with coating composition 4C' shortlyafter composition 4C' is prepared. The wet films are essentially lumpfree.

The coating compositions on all of the panels PC, P₂₄ C, and PC' areallowed to air dry and then are cured for about 1 hour at 220° C. tosmooth, essentially lump free coatings having a thickness of about 3mils. Panels from each group are subjected to the following heat, 100%condensing humidity, detergent, 5% salt spray, and water soak tests asdescribed in EXAMPLE 2(c). These tests are performed as in EXAMPLE 2(c)except where specifically indicated otherwise. The test results aregiven in the following TABLE 5.

                  TABLE 5                                                         ______________________________________                                        TEST         PC          P.sub.24 C                                                                            PC'                                          ______________________________________                                        1 hour at 538° C.                                                                   passed      passed  passed                                       1000 hours in                                                                              passed      passed  passed                                       100%                                                                          condensing                                                                    humidity                                                                      at 37.8° C.                                                            250 hours in passed      passed  passed                                       detergent                                                                     tank at 74° C.                                                         500 hours in 5%                                                                            passed      passed  passed                                       salt spray                                                                    at 35° C.                                                              24 hours in water                                                                          passed      passed  passed                                       at 93° C.                                                              ______________________________________                                    

Comparison of the above results for panels from groups PC and P₂₄ Cillustrates, that this coating composition sprayed after even 24 hoursfrom preparation cures to a durable, lump-free coating as does the samecoating composition sprayed a short time after preparation.

The following EXAMPLE 5 illustrates the invention wherein no additionalacid is used in the preparation of the coated, aluminum metaphosphate.

EXAMPLE 5 (Preparation of a Coated, Aluminum Metaphosphate)

(a) An aqueous slurry is prepared from 600 g of HB hardener availablefrom Pennwalt Company (containing about 80% by weight B-form aluminummetaphosphate and about 20% by weight A-form aluminum metaphosphate),150 g of A-form aluminum metaphosphate, and 1000 ml of water. The abovematerials are mixed for about 16 hours in a ball mill to produce aslurry containing 45.2% by weight solids and having a pH of about 2.3 atabout room temperature.

(b) With 1517 g of the slurry from part (a) immediately above is mixed525.7 g of Shepherd Brown #20 (a pigment available from the ShepherdChemical Company) to form a pigmented slurry.

(c) Next, 2042.7 g of the pigmented slurry from part (b) immediatelyabove is heated while intermittantly adding distilled water. Theintermittant addition of the water is stopped after a total of 200 ml ofwater has been added and the temperature of the pigmented slurry hasreached about 85° C. Then 8.1 ml of aqueous, 50% by weight potassiumhydroxide is added to raise the pH of the pigmented slurry to about 6while the temperature is allowed to rise to about 90° C.

Next, 314.7 g of an aqueous sodium aluminate solution (containing 41.2%by weight sodium aluminate) is slowly added dropwise to the pigmentedslurry while the slurry is stirred and the temperature maintained in therange of from 85° C. to 95° C. After the addition of the aqueous sodiumaluminate has been completed, stirring of the pigmented slurry iscontinued while the temperature of the slurry is allowed to fall to roomtemperature. The resultant composition, herein designated 5A, containingcoated aluminum metaphosphate has a 58.7% by weight solids content and apH of 7.2.

EXAMPLE 6 (Preparation of a Curable Coating Composition and a CuredCoating Therefrom)

(a) An aluminum metaphosphate hardener herein designated 6A is preparedby mixing the components set forth in the following TABLE 6.

                  TABLE 6                                                         ______________________________________                                                            Hardener 6A                                                                   (pbw)                                                     ______________________________________                                        Composition 5A of EXAMPLE 5(c)                                                                      451.9                                                   Water                 68.1                                                    Aqueous 50% KTPP*     20.0                                                    Strodex PK-90*        3.5                                                     Strodex SEK-50*       6.2                                                     Foamaster VL*         2.3                                                     Attagel 40*           14.0                                                    Micromica C-1000*     45.0                                                    Minusil-10*           20.0                                                    ______________________________________                                         *Described in EXAMPLE 2(a).                                              

(b) Three hundred parts by weight of hardener 6A is mixed withsufficient aqueous 50% by weight potassium hydroxide to raise the pH ofhardener 6A to about 9.5.

Next a curable coating composition containing 46% by weight solids,herein designated 6C, is prepared by mixing the components set forth inthe following TABLE 7.

                  TABLE 7                                                         ______________________________________                                                          Composition 6C                                                                (pbw)                                                       ______________________________________                                        Hardener 6A of EXAMPLE 6(b)                                                                       300                                                       Water               20.8                                                      Aqueous sodium silicate*                                                                          257.6                                                     Aqueous potassium silicate*                                                                       128.8                                                     Micromica C-3000*   21.6                                                      ______________________________________                                         *Described in EXAMPLE 2(b)                                                    **Mica available from English Mica Corp.                                 

(c) A steel panel is sprayed to a wet film thickness of about 6 milswith coating composition 6C shortly after composition 6C is prepared.The wet film is essentially lump-free.

The coating composition is allowed to air dry and then is cured at 220°C. for 1 hour to a smooth, substantially lump-free coating having athickness of about 3 mils.

EXAMPLE 7 (Preparation of a Coated, Aluminum Metaphosphate)

(a) An aqueous slurry is prepared containing 24.3% by weight HBhardener, 6.2% by weight A-form aluminum metaphosphate, 23.% by weightShepherd Brown #20 and 45.8% by weight water by milling the componentsin a ball mill for about 16 hours.

(b) An aqueous solution of sodium metaborate is prepared by dissolving50 g of sodium metaborate, Na₂ B₂ O₄.8H₂ O, in 100 ml of water. 750 g ofthe slurry from part (a) immediately above is heated to a temperature inthe range of 85° C. to 90° C. Then enough of the aqueous sodiummetaborate solution is added to the slurry to initially raise the pHinto the range of from 6 to 8. Next the aqueous sodium metaboratesolution and an aqueous, 85% by weight phosphoric acid solution aresimultaneously added dropwise to the slurry over a period of about 15minutes while the slurry is stirred and the temperature maintained atabout 85° C. The simultaneous dropwise addition is carried out so as tomaintain the pH of the slurry in the range of about 6 to 8. Thephosphoric acid addition is stopped just before the addition of thesodium metaborate is stopped, and the remaining several drops of sodiummetaborate are added to adjust the pH to 7.5. A total of 12.2 g of theaqueous, 85% by weight phosphoric acid solution is used during thesimultaneous addition. All 50 g of the sodium metaborate is used duringthe described initial pH adjustment and simultaneous dropwise addition.The resultant composition, herein designated 7A, contains 51.6% byweight solids and has a pH after cooling to about 22° C. of 7.1.

EXAMPLE 8 (Preparation of a Curable Coating Composition and a CuredCoating Therefrom)

(a) An aluminum metaphosphate hardener, herein designated 8A, isprepared by mixing the components set forth in the following TABLE 8.

                  TABLE 8                                                         ______________________________________                                                            Hardener 8A                                                                   (pbw)                                                     ______________________________________                                        Coated aluminum metaphosphate, 7A,                                                                  264.0                                                   of Example 7(b)                                                               Aqueous 50% KTPP*     9.2                                                     Strodex PK-90*        7.3                                                     Strodex SEK-50        2.8                                                     Foamaster VL*         1.1                                                     Minusil-10*           9.2                                                     Micromica C-100*      41.8                                                    ______________________________________                                         *Described in EXAMPLE 2(a).                                              

(b) Hardener 8A is mixed with 10.2 pbw aqueous, 50% by weight potassiumhydroxide to a pH of 9.8. Next a curable coating composition, hereindesignated 8C, is prepared by mixing the components set forth in thefollowing TABLE 9.

                  TABLE 9                                                         ______________________________________                                                          Composition 8C                                                                (pbw)                                                       ______________________________________                                        Hardener 8A of Example 8(b)                                                                       339.9                                                     Water               10.9                                                      Aqueous sodium silicate.sup.1                                                                     247.2                                                     Micromica C-3000.sup.2                                                                            10.2                                                      Attagel 40.sup.3    6.8                                                       ______________________________________                                         .sup.1 Described in EXAMPLE 2(b).                                             .sup.2 Described in EXAMPLE 4(b).                                             .sup.3 Described in EXAMPLE 2(a).                                        

(c) Several steel panels, collectively designated PC_(o), are sprayed toa wet film thickness of about 6 mils with coating composition 8C shortlyafter composition 8C is prepared. The wet films contain a few lumpswhich, however, decrease considerably in size upon air drying. Afterallowing the films to air dry at ambient temperature, the coatingcompositions are cured for about 1 hour at 220° C. to coatings having athickness of about 3 mils and containing a few small lumps moreappropriately characterized as small grains.

Several steel panels, collectively designated PC₂₄, are sprayed to a wetfilm thickness of about 6 mils with coating composition 8C about 24hours after composition 8C is prepared. The wet films are substantiallylump-free. These coating compositions are allowed to air dry at ambienttemperature and then are cured for about 1 hour at 220° C. tosubstantially lump-free coatings having a thickness of about 3 mils.

Panels from each group are subjected to the following heat, 100%condensing humidity, detergent, 5% salt spray, and water soak tests asdescribed in EXAMPLE 2(c). These tests are performed as in EXAMPLE 2(c)except where specifically indicated otherwise. The test results aregiven in the following TABLE 10.

                  TABLE 10                                                        ______________________________________                                        TEST             PC.sub.o    PC.sub.24                                        ______________________________________                                        1 hour at 538° C.                                                                       passed      passed                                           575 hours in 100% condensing                                                                   passed      passed                                           humidity at 37.8° C.                                                   Detergent tank at 74° C.                                                                failed at about                                                                           failed at about                                                   150 hours   150 hours                                        5% salt spray at 35° C.                                                                 failed at about                                                                           failed at about                                                   350 hours   350 hours                                        24 hours in boiling water                                                                      passed      passed                                           ______________________________________                                    

The above results illustrate that this coating composition sprayed aftereven 24 hours from preparation cures to a reasonably durable,substantially lump-free coating.

The following EXAMPLE 9 illustrates the invention using awater-dispersible rather than a water-soluble metal aluminate.

EXAMPLE 9 (Preparation of a Coated, Aluminum Metaphosphate)

(a) 200 g of essentially insoluble calcium aluminate, CaAl₂ O₄, ismilled in a ball mill with sufficient water to produce apaste-containing 30.5% by weight solids.

An aqueous slurry is prepared containing 24.3% by weight HB hardener,6.2% by weight A-form aluminum metaphosphate, 23.7% by weight ShepherdBrown #20 and 45.8% by weight water by milling the components in a ballmill for about 16 hours.

750 g of the aqueous slurry is placed in a steel beaker fitted with anair motor attached to a high lift blade, a heating element, and pH andtemperature probe. The slurry is agitated and heated to a temperature ofabout 60° C. at which temperature 2 ml of an aqueous, 50% by weightsolution of potassium hydroxide is added so as to increase the fluidityof the slurry. Next the slurry is heated to 85° C. at which pointaddition of the calcium aluminate paste is begun. The calcium aluminatepaste is added to the slurry over a period of 10 minutes while the pH ismaintained in a range of from 7 to 8 by the simultaneous addition of asmall amount of aqueous, 85% by weight phosphoric acid. When theaddition of calcium aluminate paste and phosphoric acid is complete, thetotal amount of the calcium aluminate paste added to the slurry is 63.9g, the total amount of 85% by weight phosphoric acid added is 2.7 g, andthe pH at about 85° C. is 7.6. Agitation of the slurry is continuedwhile the slurry is allowed to cool to about room temperature. Theresulting composition containing coated aluminum metaphosphate is hereindesignated 9A.

EXAMPLE 10 (Preparation of a Curable Coating Composition and a CuredCoating Therefrom)

(a) An aluinum metaphosphate hardener, herein designated 10A, isprepared by mixing the components set forth in the following TABLE 11.

                  TABLE 11                                                        ______________________________________                                                            Hardener 10A                                                                  (pbw)                                                     ______________________________________                                        Coated aluminum metaphosphate, 9A,                                                                  233.1                                                   of Example 9(b)                                                               Water                 25.0                                                    Strodex PK-9*         1.6                                                     Strodex SEK-50*       2.8                                                     Foamaster VL*         1.1                                                     Minusil-10*           9.2                                                     Micromica C-1000*     41.8                                                    ______________________________________                                         *Described in EXAMPLE 2(a).                                              

(b) Hardener 10A is mixed with 6.3 pbw aqueous, 50% by weight potassiumhydroxide to raise the pH to 9.8. Next a curable coating composition,herein designated 10C, is prepared by mixing the components set forth inthe following TABLE 12.

                  TABLE 12                                                        ______________________________________                                                          Composition 10C                                                               (pbw)                                                       ______________________________________                                        Hardener 10A of Example 10(b)                                                                     320.9                                                     Water               10.0                                                      Aqueous sodium silicate*                                                                          247.2                                                     Aqueous potassium silicate*                                                                       123.6                                                     Micromica C-3000**  10.2                                                      Attagel 40**        9.1                                                       ______________________________________                                         *Described in EXAMPLE 2(b).                                                   **Described in EXAMPLE 4(b).                                                  ***Described in EXAMPLE 2(a).                                            

Several steel panels, collectively designated _(o) PC are sprayed to awet film thickness of about 6 mils with coating composition 10C shortlyafter composition 10C is prepared. The wet films are smooth andessentially lump-free. The films are allowed to air dry at ambienttemperature and then are cured at about 220° C. for about one hour todurable, essentially lump-free coatings of approximately 3 milsthickness.

Several steel panels, collectively designated PC₆₀₊, are sprayed withcoating compositions 10C after 60 hours from when coating composition10C is prepared. The films are allowed to air dry at ambient temperatureand then are cured at 220° C. for about 1 hour to durable, essentiallylump-free coatings of approximately 2.5 mils thickness.

Panels from each group are subjected to the following heat, 100%condensing humidity, detergent, 5% salt spray, and water soak tests asdescribed in EXAMPLE 2(c). These tests are performed as in EXAMPLE 2(c)except where specifically indicated otherwise. The test results aregiven in the following TABLE 13.

                  TABLE 13                                                        ______________________________________                                        TEST             .sub.o PC PC.sub.60+                                         ______________________________________                                        1 hour at 538° C.                                                                       passed    passed                                             575 hours in 100%                                                                              passed    passed                                             condensing humidity                                                           at 37°8 C.                                                             575 hours in detergent                                                                         passed    failed at about                                    tank at 74° C.      50 hours                                           575 hours in 5% salt                                                                           passed    passed                                             spray at 35° C.                                                        24 hours in      passed    passed                                             boiling water                                                                 ______________________________________                                    

Comparison of the above results for panels from groups _(o) PC and PC₆₀₊illustrates that this coating composition containing hardener preparedusing water-dispersible calcium aluminate when sprayed after even 60hours from preparation cures to a durable, lump-free coating as does thesame coating composition sprayed a short time after preparation.

What is claimed is:
 1. A method of preparing a coated, metal condensedphosphate comprising:(A) combining an aqueous slurry of metal condensedphosphate with (B) an aqueous metallate selected from the groupconsisting of metal aluminate, metal borate and a mixture thereof, saidmetallate in an amount sufficient to provide a coating on said metalcondensed phosphate of from about 0.1 percent to about 50 percent byweight based on the combined weight of said metal condensed phosphateand said coating, while maintaining the pH of said slurry in a range offrom about 4 to about
 10. 2. The method of claim 1 wherein thetemperature of said slurry is maintained in a range of from about 50° C.to about 95° C.
 3. The method of claim 2 wherein the pH of said slurryis maintained in said range by addition of an acid to said slurry. 4.The method of claim 3 wherein at least part of said addition of acid iscarried out simultaneously with addition of said aqueous metallate. 5.The method of claim 4 wherein the pH of said slurry is maintained in therange of about 6 to about 8 during combination of said slurry with saidaqueous metallate.
 6. The method of claims 1 or 4 wherein said metallatecomprises a water-soluble metallate.
 7. The method of claim 6 whereinsaid water-soluble metallate comprises a water-soluble metal aluminate.8. The method of claim 7 wherein said water-soluble metal aluminatecomprises sodium aluminate.